Acute ischemic stroke (AIS) is caused by a sudden blockage to one of the large intracranial vessels in the brain by a blood clot that moves through the intracranial vessels and where it becomes lodged within a narrowing vessel thus cutting off blood flow to a portion of the brain. AIS is usually a devastating disease that unless quickly treated to re-establish blood flow to the brain can result in significant impairment of a patient's brain function.
Importantly, recent studies including “Randomized Assessment of Rapid Endovascular Treatment of Ischemic Stroke” published on Feb. 11, 2015, at NEJM.org, and “Stent-Retriever Thrombectomy after Intravenous t-PA vs. t-PA Alone in Stroke” published on Apr. 17, 2015, at NEJM.org, have shown that patient outcome is significantly improved by removing the blood clot quickly and safely. The effect of these studies has been that endovascular treatment of stroke is now the standard of care as endorsed by the American Heart Association/American Stroke Association (see “2015 AHA/ASA Focused Update of the 2013 Guidelines for the Early Management of Patients With Acute Ischemic Stroke Regarding Endovascular Treatment—A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association; www.stroke.ahajournals.org: ((Stroke. 2015; 46:000-000.).
Recanalization are procedures that are used to remove the blood clot by guiding recanalization equipment through the blood vessels of the brain under x-ray guidance. In a recanalization procedure, access to the vascular system is typically obtained in the patient's groin region by entering the common femoral artery and advancing a steerable wire within a coaxial balloon guide catheter through the vascular system to access the carotid artery. Often there may be a diagnostic preshaped catheter with the balloon guide catheter to allow access to the relevant branch from the aorta.
For the purposes of general illustration, and with reference to FIG. 1, a simple schematic representation of a section of brain vascular anatomy is shown. As shown in FIG. 1, the ophthalmic segment of the carotid artery OA is shown having a tortuous segment 5. Distal to the ophthalmic artery is the intracranial internal carotid artery IICA, the anterior cerebral artery ACA, the M1 segment of the middle cerebral artery and the M2 segment of the middle cerebral artery. A blood clot or occlusion Y is shown within the M1 segment.
Usually, when the physician has entered the carotid artery with the catheter, the intracranial occlusion is confirmed by injecting a bolus of xray dye into the patient and taking xray pictures that then assist the physician in accurately determining the location and size of the occlusion in order that the microwire and microcatheter are advanced to the desired position relative to the occlusion.
At this stage, when a microwire has been advanced to the clot, there are varying technologies and techniques that can be used to recanalize the blood vessel.
The most commonly used technology uses a self-expanding stent or stent retriever as a means to withdraw the thrombus responsible for the occlusion. In this procedure, a microcatheter with the help of the microwire is advanced beyond the clot using xray guidance. A guide catheter having a balloon will typically also be advanced to a position in the internal carotid artery in the neck. Subsequently, the self-expanding stent is advanced into the microcatheter and is gently deployed across the occlusion by withdrawing the microcatheter and unsheathing the stent. Usually after deployment of the stentriever there is some degree of forward flow. After waiting for a few minutes the thrombus gets entangled in the tines of the stent retriever. At this stage, the balloon in the guide catheter is inflated to prevent antegrade (forward) flow in the vessels, and the stent is withdrawn while applying suction (reversal of flow direction) at the guide catheter in the neck. The clot is thereafter removed through the guide catheter.
This approach has a few disadvantages including that the procedure does not always work for various reasons. For example, depending on the anatomy of the patient, applying suction pressure at the neck sometimes does not get transmitted to the clot particularly if there are other branches (from a patent circle of Willis) that may provide blood flow in a way that the suction pressure is not transmitted to the occluded vessel. In addition, there is also a potential for the clot to fragment and move into distal vessels. Further still, managing and placing balloon guide catheters can be technically challenging and potentially time consuming. In addition, self-expanding stents are expensive.
As a result, there is a move towards making catheters with a larger inner lumen that are flexible enough that they can be advanced into the brain vessels (typically the middle cerebral artery) and into a position such that the catheter can be used to directly suck the clot through the catheter rather than using an expandable stent. This procedure overcomes some of the disadvantages including applying suction pressure directly to the clot in a manner that is not dependent on the patient's anatomy. In addition, the costs will be lower if a stent is not used and this procedure may also save time. Local suction may also reduce the likelihood of clot fragmentation.
However there are significant limitations to the current generation of large bore distal access catheters (DACs). One of these is the ability of these catheters to move through those blood vessels having a significant curvature. In particular, it is known that most strokes occur in older people where the tortuousity of certain blood vessels may be greater than the same blood vessels of a younger person due to age-related changes in the vasculature. Also, the inner surface of the vessels in an older person may not be as smooth because of atherosclerotic disease. Importantly, both of these conditions can compound the problem of moving catheters through the vasculature of a stroke patient.
As shown in FIGS. 2 and 2A, the procedure of inserting a large bore distal access catheter 18 typically involves the manipulation of a tri-axial system comprising a microwire 12a inside a microcatheter 12b inside a distal access catheter (DAC) 18 through the vasculature. Initially, the microwire and microcatheter are placed in the carotid artery in the neck and are then advanced to beyond the clot. Using the microwire and microcatheter as support, the distal access catheter is then advanced forward to the desired position adjacent the clot. In certain locations, this procedure does not often work properly as the distal access catheter gets stuck around tight bends especially in the ophthalmic bend of the internal carotid artery as shown in FIG. 2A. That is, the outer edge 18a of the DAC may be pushed into the outer surface of the ophthalmic bend which often leads to it becoming stuck. This problem is compounded by the difference in diameter of the distal end of the DAC relative to the diameter of the microcatheter 12b that creates a gap 17. If the DAC gets stuck, this results in delays.
One solution that has been proposed to address this problem of the DAC getting stuck is to deploy the stentriever through the microcatheter and use the friction of the stentriever against the vessel and clot as leverage to be able to manipulate the distal access catheter through the bend. That is, by a combination of gently pushing and pulling the stentriever and DAC, the DAC can be advanced around the tight curvature of the ophthalmic bend. While this can be successful, this is disadvantaged by the significant cost increase of using a stent and it can also be time consuming. Moreover, given the differences in size between the DAC and microcatheter, the gap 17 may prevent forward movement of the DAC over the microcatheter as the distal end of the DAC cannot be bent enough within the tight curve.
Accordingly, there has been a need for a system that in particular aids the movement of a larger bore catheter (i.e. a distal access catheter) through the vasculature and particularly regions of the vasculature having a high tortuousity.